A sensor that detects a deformation caused by a contact of an object with another object includes a tactile sensor, a bending sensor and the like, and is widely used in various fields. The tactile sensor detects intensity, a position, a direction and the like of the contact and the bending sensor detects a bending deformation. The sensors are applied to, for example, a hand and a skin of a robot, and information such as the intensity, position, direction and the like of the contact obtained from the sensors is utilized as information to determine next action of the robot when controlling a motion of the robot and corresponding to an external pressure. There are various proposals with respect to the sensor and a method of making the sensor (in Patent Documents 1 to 3).
Patent Document 1 discloses a pressure detection device comprising: a buffer member deformable by pressurizing and depressurizing including a magnet, and a sensor assembly for detecting a change in a magnetic field caused by deformation of a buffer portion with a magnetic sensor. The magnet present in the buffer member may be one large magnet (FIG. 1 of Patent Document 1) or small magnets uniformly dispersed (FIG. 7 and the like of Patent Document 1). In case of the one large magnet, there is a problem that it is difficult to detect the deformation due to touching, and a foreign body sensation is caused due to touching it. On the other hand, in case of the small magnets uniformly dispersed, since a phenomenon of canceling magnetic forces between magnet particles occurs even if the direction of the magnetic force of each magnet is the same as one another and the magnet near a contact surface moves but the magnet present inside the buffer member is difficult to move, there is a problem that detection sensitivity is poor when the external force is small and the deformation is very small.
Patent Document 2 discloses a detecting device comprising a viscoelastic magnet obtained by kneading and molding a magnet material and a viscoelastic material and magnetic-flux detecting means for detecting a change in a magnetic flux density vector due to deformation of the viscoelastic magnet. In the detecting device of Patent Document 2, since the magnet material is kneaded in the viscoelastic material, the magnet material is uniformly dispersed. Therefore, since a phenomenon of canceling magnetic forces between the magnet particles occurs and the magnet near a contact surface moves but the magnet present inside the buffer member is difficult to move, there is a problem that detection sensitivity is poor when an external force is small and the deformation is very small as described in Patent Document 1.
Patent Document 3 discloses a magnetostrictor comprising (a) at least one apparatus for generating a magnetic field, and (b) at least one molding member formed from a porous polymer containing a ferromagnetic particle. Patent Document 3 discloses that the porous polymer containing the ferromagnetic particle is used as a vibration sensor, but does not show a performance data such as a sensor sensibility. In addition, Patent Document 3 does not disclose a concrete method of making the porous polymer and properties of the porous polymer. Therefore, there is ample room for further improvement by optimizing the manufacturing method and the properties such as a cell diameter, specific gravity and the like of the porous polymer.